Turbine inlet (compressor discharge) temperatures for gas turbine engines such as industrial gas turbines, which are used for pumping, the generation of electricity and the like are extremely high, being on the order of 1300-1400.degree. C. In order to withstand such extreme temperatures, it has been the practice to provide metallic turbine blades and vanes with internal cooling. That is, such blades and vanes are provided with a very intricate network of internal passages through which compressor discharge cooling air flows, to remove heat from the interior of the blade or vane. The external surfaces of such components are cooled with cooling air discharged from the internal passages, which flows as a film over the surface of the component to carry away heat therefrom and then enters the flow of working fluid exiting the engine's combustor. Such blades and vanes are also coated with various highly temperature resistant ceramic and metallic coatings, which further aid these components in withstanding the extreme temperatures encountered at the turbine inlet.
Such internally cooled blades and vanes tend to be very expensive to produce owing in large measure to the complexity of the internal cooling air passages and the costly materials employed in the coatings. Moreover, such blades and vanes require very high volumes of cooling air to withstand the extreme turbine inlet temperatures set forth above and therefore detract significantly from the overall efficiency of the engine in that such cooling air is unavailable to support combustion within the engine and therefore cannot be used directly by the engine to produce power. Furthermore, the relatively high volumes of cooling air which enter the flow of working fluid exiting the engine's combustor, react with the products of combustion to produce excessive quantities of nitrous oxides, undesirable pollutants which are sought to be minimized.
Efforts to overcome these deficiencies in state-of-the-art metallic vanes have led to the suggestion of vanes formed entirely of ceramic, with a simple, hollow interior cooled by an impingement of cooling air against the inner surface of the vane. Such a simple interior cooling arrangement is significantly less costly to manufacture than the complex arrangements of cooling passages in current metallic vanes. Moreover, the ceramic material itself from which the blade is formed, typically a silicon nitride or similar material, is less costly than the rather exotic metallic materials employed in state-of-the-art vanes. However, such ceramic vanes typically have coefficients of thermal expansion far less than those of metallic materials from which the associated stators are constructed. Thus, mounting such vanes to such metallic stators has heretofore been impossible without the vanes loosening from their mounts due to the differing rates at which the vanes and stator structures expand and contract during the operation of the engine.